The present invention relates to a camera for optoelectronically scanning any desired scene, wherein the camera includes: (a) a line image sensor which is displaceable through an image field of a scene located in the major opto-electronic beam path and perpendicularly to the line direction of the sensor; and (b) a moving device including a carrier for displacing the line image sensor.
The fields of use for such a camera include image transmission, image processing and image evaluation, with such uses being limited most of the time to static scenes whose content does not change during the scanning time, i.e. over a period of a few seconds. Line image sensors and area image sensors are commercially available as integrated semiconductor components for use in electronic cameras.
In a known electronic camera disclosed in East German Pat. No. 134,031, a mechanical device for moving a line image sensor is composed of a movable carrier on which the line image sensor is fastened, a guide for the carrier which assures accurate tracking of the line image sensor across the image field, and a gear assembly including a drive for synchronously moving the carrier. The carrier and its guide are composed, for example, of a micro roll table with a circuit board mounted thereon, the gear assembly being in the form of a precision spindle and spindle nut, with the drive being a stepping motor.
Such a microroll table (type ND) has been described, e.g., on page 50 of the leaflet "Walzfuhrungen" (issue 100a/06, 1985) by Schneeberger GmbH Maschinenfabrik, Graefenau, Germany.
Alternatively, it is also known to use a metal band drive, as disclosed for example in European Pat. No. 0,131,814, for moving the line image sensor.
The moving device assures a certain longitudinal displacement of the carrier over a given displacement range which is generally limited by end switches at the ends of the displacement range.
Image sensors contain photosensitive solid state devices which in a line image sensor are arranged along a line, whereas in an area image sensor the configuration is two-dimensional on an area.
Line image sensors and area image sensors are described as examples in a leaflet entitled "Optoelektronics Data Book 1984", pp. 2-29 to 2-40 (line image sensor TC 103) and pp. 2-53 to 2-54 (area image sensor TC 102/202), published by Texas Instruments Deutschland GmbH.
According to this leaflet the line image sensor contains 2048 photosensitive elements with a distance of the centerlines of nearly 12.7 .mu.m so that the length of the sensor is nearly 26 mm.
The area image sensor (TC 202) contains 292 lines with 390 photosensitive elements each, the aspect ratio of the entire sensor area being 4 to 3 and the image diagonal 11 mm long.
Accordingly, the horizontal and vertical centerline distances of the photosensitive elements are about 22.5 .mu.m.
While it is possible to manufacture a line image sensor to include several thousand sensor elements, the number of sensor elements per edge of an area image sensor is limited, for technological reasons, to several hundred. Since the sensor element dimensions generally are comparable in both types of sensors, an associated image field for the area image sensor is significantly smaller than for the line image sensor and the area image sensor has a much poorer geometric resolution for an associated image field. The two edge dimensions of a field to be reproduced and scanned by a line image sensor correspond, inter alia, to the length of the line image sensor and the length of the displacement range. Such a field to be reproduced is called an image field.
Hereinforth a line scan image sensor is called a line sensor, and an area image sensor is called an area sensor respectively.
German Offenlegungsschrift (laid-open patent application) No. 3,433,684 discloses an apparatus for generating digital image information. The imaging beam path of this device is directed into two mutually perpendicular directions by means of a pivotal mirror. In the first position of the pivotal mirror, a primary beam path is produced in which the image field is disposed in the plane of movement and in the displacement range of the line sensor. In the second position of the pivotal mirror, a view finder beam path reproduces the image field on a ground observation glass.
This device has the characteristics of ground glass observation via a deflection mirror as known from the prior art reflex photography, namely: (1) brightness and contrast of the ground glass image are a function of the field of the scene; and (2) the ground glass image has dimensions in the range of centimeters, requiring observation through a magnifying glass, with lateral inversion of the image. In the intended special application of the described device for the transmission of transparent master images with adjustable illumination, these characteristics are not necessarily a drawback but they make universal application of such a device for scanning any desired scenes more difficult.
European Pat. No. 0,124,098 discloses an image scanner having a mechanically movable line sensor. An image frame is optically reproduces by means of a projector which projects light onto a document to be scanned. The image frame permits correct positioning, size adjustment and focusing. The projector is composed of an intense light source, a slide for the image frame embedded in optical components to block out heat and concentrate the light, with the slide being disposed in the plane of the image field next to the linear array on the carrier. For this purpose, the carrier has been made longer in length.
The moving device here has an extended displacement range, i.e. the guide and the spindle, in particular, have been extended so that, at one time, the slide containing the above-mentioned optical components is positioned entirely in the image field and, at another time, the linear array scans the image field, thus providing a parallax-free common beam path for scanning and projection.
Although such a device avoids the drawbacks of ground glass oberservation, it is usable only for scanning reflected images or documents, respectively. Another drawback is the development of intense heat by the projector in the immediate vicinity of the line sensor.
In East German Pat. No. 134,031, mentioned above, the imaging camera has a mechanically movable line sensor and an area sensor in which two separate image fields are produced by a beam dividing mirror for the line sensor and for the area sensor and the area sensor is connected with a monitor by means of a video circuit and thus constitutes an electronic view finder. The necessary image field reduction for the area array is here effected in a known manner via an intermediate image, a light concentrating Fresnel lens and an additional lens.
The possibility of observing the field of the scene even with low light, with low contrast, with a visually unfavorable spectral range and with a difficultly accessible or remote camera location are advantages of the described camera, but a drawback inherent in it is that the low geometric resolution of the area sensor, although permitting image field setting, makes precise focusing more difficult.
It is also known to equip an electronic camera with a device for scanning in selective spectral regions. For example, the brochure No. 500/10M/5-84 of EIKONIX Corporation, Bedford, Massachusetts, depicts an electronic camera having a mechanically movable line sensor and a ground glass view finder, containing a filter wheel with various filters. These filters are selectively inserted into the beam path by rotating the filter wheel by means of a controllable drive.
An electronic camera which is intended for scanning of any desired scene is generally equipped with a connecting device for exchangeable photographic lenses.
The controllable components of such an electronic camera, for example, the moving device, the pivotal mirror drive and the filter wheel drive as well as the operating circuit for the line sensor are connected with a control unit via interface circuits to coordinate the functions of the individual components. The line sensor is also connected via video and analog/digital circuits, with an image transmitting or image processing device. Generally, the control unit and the image processing unit are realized in a digital computer.
Operating and video circuits for line sensors or area sensors are commercially available. For instance, Thomson-CSF, Boulogne-Billancourt, France, describes this type of circuit in a leaflet entitled "Electronic Modules for Charge-coupled Devices", April 1984. Also in the brochure mentioned before of Texas Instruments Deutschland GmbH such modules are described on pp. 2-55 to 2-58.
Operating circuits for moving devices are commercially available. For example, the brochure PKS Digiplan Ansteuerund Positioniergerate fur Schrittmotoren of BAUTZ, Weiterstadt-Darmstadt, Germany, depicts at page 6 and 7 an operating circuit for stepper motors (SD 2/3).